AD9851 Initialization

Hi, i am trying to program  DDS AD9851, but i can’t start output frequency generation.

I use 20 MHz generator as reference clock and 6x multiplier to get 2 MHz output.

According to the on-line calculator http://designtools.analog.com/dt/dds/ad9851.html  i got following values “W0 0xBA”, “W1 0x62” “W2 0x22” “W3 0x20” “W4 0x80”.

I made hardware configuration for serial load enable word W0.

To reset DDS default values i make this  workflow:

1)pull up Reset line;

2) 10 microseconds  delay;

3) pull down Reset line;

4)pull up W_CLK line;

5)pull down W_CLK line;

6)pull up FQ_UD line;

7)pull down FQ_UD line;

// reset device and enable serial load mod;

8) pull down Serial line and make for 40 times pull up/down W_CLK line;

9)pull up FQ_UD line;

10)pull down FQ_UD line.

To load calculated data (w0-w4) i make this workflow:

1)pull up Reset line;

2) 10 microseconds  delay;

3) pull down Reset line;

4)pull up W_CLK line;

5)pull down W_CLK line;

6)pull up FQ_UD line;

7)pull down FQ_UD line;

// i resetting device to clear phase accumulator +phase offset and then re enable serial load mode

8) transmit W0-W4 by right shift in series and sending current byte lsb.

9)pull up FQ_UD line;

10)pull down FQ_UD line;

Оn oscilloscope i see that the right data load to the DDS,but i don’t see any output generation. Could you check my workflow for errors please.

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  • 0
    •  Analog Employees 
    on Jan 17, 2013 5:46 PM over 8 years ago

    Hi EugeneG,

    Since the data transfers are done in serial, it is expected that information rate would depend on the serial clock and the number of bits needed for that information. The only way to speed it up is to use shorter pulses on the W_CLK, FQ_UD, and DATA, but make sure that it doesn't run faster than what is specified by the data sheet.

    Regards,

Reply
  • 0
    •  Analog Employees 
    on Jan 17, 2013 5:46 PM over 8 years ago

    Hi EugeneG,

    Since the data transfers are done in serial, it is expected that information rate would depend on the serial clock and the number of bits needed for that information. The only way to speed it up is to use shorter pulses on the W_CLK, FQ_UD, and DATA, but make sure that it doesn't run faster than what is specified by the data sheet.

    Regards,

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